Fuel pumps, electrically driven, are used for furnishing liquid fuel to internal combustion engines. In recent years, these fuel pumps have been mounted inside the fuel tanks of vehicles sometimes within a vertical canister which receives fuel returning from a circuit including a pressure relief and return valve. In geographic regions, where high temperatures are experienced, at least in some seasons of the year, pumping hot fuel creates problems because the fuel tends to vaporize. This is especially true with the lighter fuel which may contain alcohol or other light additives. When a fuel pump draws an inducing pressure on liquid fuel, especially hot fuel, there is a tendency for the fuel to vaporize. Vapor in a pump significantly reduces the efficiency. When a vehicle sits out in the hot sun, the temperature in a fuel tank will rise close to the vaporization point.
To alleviate this problem, and for other reasons of efficiency, one recent development has been to incorporate two pumps in series, that is, a first stage pump to draw fuel from the tank and furnish the fuel to a second stage pump which delivers the fuel to the engine.
The present invention is directed to the use of a two-stage pump and embodies an assembly using a side channel, sometimes called a lateral channel, first stage pump which draws fuel from a fuel tank and furnishes it to a main second stage pump which is preferably a positive displacement pump of the roller vane type, or a gear rotor pump where two gears, one within the other, rotate to force fuel into a vehicle system under a desired pressure. The term gerotor is applied to the gear rotor pump.
The present invention is also directed to the use of a side channel pump which is designed to remove as much vapor as possible from the fuel before it is delivered to the second stage pump as solid fuel, that is, totally liquid. In this way, the delivery of the second stage pump can be dependable and will meet the pressure and volume requirements of a particular engine.
The vapor removal is accomplished by a pump assembly in which fuel delivery from the side channel pump is central of the rotor and the liquid fuel is moved outward, as the heavier medium, by the centrifugal force, and the vapor, as the lighter medium, is moved inward by the liquid fuel. Directing components move the vapor centrally where recesses and passages are provided for the escape of the vapor from the pumping system. Meanwhile, the liquid fuel from the first stage pump is moved outwardly and introduced peripherally through a conical baffle to the inlet side of the gerotor pump. Several modifications are described for achieving the removal of vapor from the first stage pump so that the fuel delivered to the main pump free of vapor.
Other objects and features of the invention will be apparent in the following detailed description and claims in which there is set forth the invention together with details to enable a person to practice the invention, all in connection with the best mode presently contemplated for the invention.